Fabrication of CeO-MO (M = Cu, Co, Ni) composite yolk-shell nanospheres with enhanced catalytic properties for CO oxidation.

CeO-MO (M = Cu, Co, Ni) composite yolk-shell nanospheres with uniform size were fabricated by a general wet-chemical approach. It involved a non-equilibrium heat-treatment of Ce coordination polymer colloidal spheres (Ce-CPCSs) with a proper heating rate to produce CeO yolk-shell nanospheres, followed by a solvothermal treatment of as-synthesized CeO with M(CHCOO) in ethanol solution. During the solvothermal process, highly dispersed MO species were decorated on the surface of CeO yolk-shell nanospheres to form CeO-MO composites. As a CO oxidation catalyst, the CeO-MO composite yolk-shell nanospheres showed strikingly higher catalytic activity than naked CeO due to the strong synergistic interaction at the interface sites between MO and CeO. Cycling tests demonstrate the good cycle stability of these yolk-shell nanospheres. The initial concentration of M(CHCOO)·HO in the synthesis process played a significant role in catalytic performance for CO oxidation. Impressively, complete CO conversion as reached at a relatively low temperature of 145 °C over the CeO-CuO -2 sample. Furthermore, the CeO-CuO catalyst is more active than the CeO-CoO and CeO-NiO catalysts, indicating that the catalytic activity is correlates with the metal oxide. Additionally, this versatile synthesis approach can be expected to create other ceria-based composite oxide systems with various structures for a broad range of technical applications.